1. Field of the Invention
The present invention relates to a technology for generating and displaying angiogram image data, and more particularly, to an X-ray diagnostic system for generating and displaying 3D (three-dimensional) angiogram image data.
2. Description of the Related Art
There is known an X-ray diagnostic system composed of, for example, an X-ray tube and a flat panel detector (FPD) (or an image intensifier (I. I.)) disposed to both the ends of an approximately C-shaped supporter (C-arm) and an image processing device to image a blood vessel whose contrast is emphasized by a contrast medium. Generally, the X-ray diagnostic system is also called an angio apparatus and a 3D angio apparatus which permit a doctor to diagnose and treat (examine) a patient and to perform X-ray imaging by inserting a catheter into a patient.
The X-ray diagnostic system employs a method of rotation DSA (digital subtraction angiography) imaging. In the rotation DSA, first, mask images of a particular region (affected area) of the patient are collected from many different directions by rotating the C-arm in a necessary direction within the range of projection angle necessary to reconstruct the mask images to a 3D image. After the contrast medium is injected into the particular region of the patient, contrast images of the particular region are collected from many different directions by rotating the C-arm in a direction opposite to that when the mask images are collected (may be the same direction as that when the mask images are collected), and the rotation DSA imaging is performed. Then, a subtraction processing is performed to obtain the difference between 2D image data having projection angles corresponding to each other, and the 2D image data is reconstructed to 3D image, and the 3D image is displayed.
To obtain an excellent angiogram image data by the rotation DSA imaging, a timing at which the contrast of an imaging region is enhanced and the amount of the contrast medium are important factors. These factors depend on a position of a catheter, a region to be imaged (position of a region of interest) and a blood velocity, which is different depending on a patient. However, in actual 3D imaging, a predetermined delay time, which is determined based on experience values of a hospital using an apparatus, is often employed and applied to all the patients. As a result, the filled amount of a contrast medium in the interest region of a contrast image of a first frame, the filled amount of the contrast medium in the interest region of a final frame, and the amount of the contrast medium injected into a venous layer are not optimum, and thus 3D image data suitable for diagnosis cannot be always obtained.
To cope with this problem, there is disclosed a technology for setting an interest region as ROI (region interest) in previously collected images, injecting a contrast medium after mask imaging is performed, and automatically performing a fluoroscopy during a period until contrast imaging is started after the contrast medium is injected (for example, Japanese Patent Application Publication No. 2001-149360). In this technology, since an image level changes when the contrast medium flows into ROI, the contrast imaging is started by sensing the change of the image level.
Although the delay time is different depending on an examiner (position of catheter), a region, a patient (blood velocity), a symptom, and the like, when the technology disclosed in Japanese Patent Application Publication No. 2001-149360 is not used, since 3D imaging is performed using the predetermined delay time determined based on the experience values of the hospital, a 3D image suitable for diagnosis cannot be generated.
In contrast, when the technology disclosed in Japanese Patent Application Publication No. 2001-149360 is used, since the fluoroscopy must be continued during the period until the contrast imaging is started from the start of injection of the contrast medium after the mask imaging is performed, a problem arises in that the amount of exposure of a patient to an X-ray is increased. Accordingly, it is difficult to practically use the technology disclosed in Japanese Patent Application Publication No. 2001-149360.